With high power CO.sub.2 lasers, a large volume of gas flows through an optical resonator. Gas flows as part of a loop system with substantially the same supply of gas flowing into, through, out of, and back through the optical resonator. Gas flow rates on the order of 300 CFM at 100 millibars pressure are not uncommon. Efficiency of the laser decreases if gas flow is hindered. For optimum performance, efficiency and economy, large volumes of gas must be pumped through the resonator, cooled, and then recirculated through the resonator. This cycle continues again and again.
Gas emerging from the resonator is at elevated temperatures of about 200.degree. to 250.degree. C. This is caused by the electrical discharge and lasing activity in the resonator. At these temperatures, CO.sub.2 molecules become dissociated, with the resulting formation of CO and O.sub.2. The original concentration of CO.sub.2 available for lasing is reduced. CO and O.sub.2 naturally recombine but an equilibrium level is reached. Additionally, the O.sub.2 reacts with N.sub.2 in the laser to form various nitrogen oxides. Again the amount of available CO.sub.2 is reduced. This change in the original gas mixture affects the laser's performance.
Small CO.sub.2 lasers, less than about 100 watts, are sealed systems and do not have gas in a loop feedback system flowing through the resonator. Because these small CO.sub.2 lasers are sealed off and fresh gas is not introduced into the system, there has been an on-going effort to minimize CO.sub.2 gas loss. Some of these efforts have been directed to catalyzing the gas in an attempt to reassociate CO and O.sub.2 and form CO.sub.2. Platinum has been used as a catalyst, often as one of the electrodes.
As previously described, large CO.sub.2 lasers depend on the constant recirculation of relatively large volumes of gas. Because the efficiency of these lasers is determined to a great extent on an ability to maintain this recirculation, anything which impedes gas flow and reduces the flow rate is undesirable.
Suggestions of placing catalysts in the circulating gas flow path have presented numerous problems. For example, U.S. Pat. No. 4,550,409 discloses the inclusion of a catalyst unit for the purpose of reconstituting CO.sub.2 gas. To maximize catalytic effect, the surface area of the exposed catalyst must be as large as possible. In this regard, pellets of a catalyst can be suspended in a cage or basket in a densely packed configuration. This design is highly problematic for large CO.sub.2 lasers. The rate of the gas flow is severely reduced when it passes through this grouping of catalyst pellets.
Utilization of pellets creates additional problems. Because the pellets are loose they rub against each other, creating dust and powder. Loose particulate matter contaminates the laser and erodes both its efficiency and lifetime.
It would be highly desirable to provide a catalytic structure suitable for recirculating CO.sub.2 gas lasers which would not appreciably affect the flow rate of the circulating gas, and would not be a source of contamination.